Common adhesives intended for use in building construction and with flooring and floorcovering materials, such as, for example, wood plank, parquet, artificial turf, boat or other marine carpets, indoor carpet, rubber flooring, cove base, etc., are water-based emulsions based upon either acrylic or styrene butadiene (SBR) latex. Acrylic-based formulas, due to their expense and low bond strength, are generally reserved for use only when necessary for a pressure-sensitive applications, for resistance to plasticizers in pure vinyl backings or for resistance to sunlight in outdoor applications. SBR-based adhesives for use in building construction, flooring and floorcovering are, by far, the predominant type and require the addition of a tackifier to develop bond strength and a proper modulus.
The traditional means of producing an adhesive of this type is to emulsify the SBR latex to form a latex emulsion. Additional constituent components, such as, for example, process oil, tackifying resins, mineral fillers, etc., are also emulsified. The latex emulsion is then added to the constituent component emulsion under various heat and pressure conditions to form the adhesive.
The adhesives produced by the traditional method have several associated disadvantages, such as, for example, poor water resistance, slow drying, high volatile organic compound content and limitations on the final solids content of the adhesive. These disadvantages are generally due to the use of emulsifiers and thickeners in forming the adhesive. Emulsifiers and thickeners are generally water-soluble compounds that remain in the dried adhesive and tend to adversely affect the water resistance and durability of the resultant adhesive bond. Water soluble compounds also tend to retard the drying rate of the water-based adhesive. Moreover, using a method in which all constituent components are emulsified prior to mixing severely limits the solids content of the final product. It is particularly desirable to produce adhesives having a high solids content due to their superior bonding and drying characteristics.
It is also desirable to eliminate the presence of volatile organic compounds (VOC) generally present in traditional adhesives of the type described above VOCs are generally used to dissolve the tackifying resins which are incorporated into the adhesive to develop bond strength and an appropriate modulus. Since these resins are generally solid at room temperature, they must be liquified in order to be incorporated into the constituent component emulsion. This is usually done by dissolving the resin in an organic solvent carrier. Organic solvents are usually quite volatile and may have adverse effects on the environment due to their contribution to air pollution. VOCs also degrade the performance of the resulting adhesive by slowing down curing time, swelling and weakening the rubber component, shortening the life of the applied product and raising the level of emulsifier required for emulsion stability, which, in turn further degrades the adhesive. The use of organic solvents to produce adhesives, in some cases, also requires the use of expensive solvent recovery equipment required by government regulation and has the further disadvantage of exposing employees to the potentially harmful organic solvents.
VOCs are also incorporated into latex-based adhesives to improve their freeze resistance. Because traditionally formulated SBR-based adhesives have a high water content, they usually have poor freeze resistance. Manufacturers have sought to overcome the poor freeze resistance by introducing VOCs such as methanol and glycol to lower the freezing point of SBR-based adhesives. However, the addition of these VOCs results in many of the same disadvantages set forth above. In order to overcome the disadvantages associated with the use of VOCs for improved freeze resistance, some manufacturers have attempted to substitute non-volatile compounds such as sorbitol to improve freeze resistance. While freeze resistance may be improved in this manner, the water resistance of adhesives using non-volatile water-soluble compounds such as sorbitol is adversely affected.